With liver damage, especially cirrhosis of the liver, intravenous blood flow from the portal vein through the liver to the hepatic vein is reduced. An increase in blood pressure results on the portal vein side, which can result in esophageal varices, i.e., varicose veins in the area of the esophagus. If the latter break, the danger exists of the patient bleeding to death. It is known to perform a portocaval, mesocaval or splenorenal anastomosis to reduce blood pressure, i.e. to perform a connection by anastomosis of the portal venous trunk and the inferior vena cava of the intestinal vein (superior vena senterica) or between splenic vein and renal vein. As a result, a reduction of pressure in the described portal hypertension takes place.
If only one such connection (shunt) is inserted, the latter can again close. A certain size of the shunt lumen is operatively not clearly able to be predetermined. Therefore, the shunt now is reliably kept open by inserting a stent in the form of a cylindrical lattice-stent preferably flexible around its axis. In an emergency, a shunt with a large diameter is inserted for quick reduction of the high pressure of the portal vein to achieve a quick and sufficient pressure reduction and thus stoppage of the bleeding of the varices. But the blood flowing through this shunt flows without purification through the liver into the brain, so that, by substances not filtered out from the blood, such as ammonia, possibly also amines and phenol elements, cerebral contamination and thus hepatic encephalopathy and thus the reduction or considerable impairment of the cerebral function of the patient can result. Also, the size of a suitable stent diameter is in principle not to be foreseen, since the correctly delimited size, between a relatively large diameter to avoid high pressure of the portal vein, on the one hand, and, on the other hand, a reduced diameter, to be able to incorporate as little unpurified blood as possible through the liver and to subject as large a portion as possible of the blood to liver purification, depends on different factors, such as, for example, the viscosity of the blood, and therefore is difficult to determine.